In the surgical treatment of spinal disorders such as scoliosis, numerous systems for attempting to correct such conditions have been devised. These systems usually include a pair of elongate members, typically either rods or plates, placed posterior-laterally on opposite sides of the vertebral column. Each rod/plate is attached to the spine with various attachment devices, such as pedicle screws, spinous process hooks, sublaminar hooks and pedicle hooks.
The strength and stability of a dual rod or plate assembly can be increased by coupling the two rods or plates with a cross-brace or transconnector which extends across the spine, substantially horizontal/perpendicular to the longitudinal axes of the rods or plate. The simplest situation in which a transconnector can be used occurs when the two rods or plates are geometrically aligned. In this case, the two rods or plates are axially parallel to each other, i.e., there is no rod/plate convergence or divergence between the rods in the medial-lateral direction, over the extent of the lengths of the rods. Also, the rods/plates have the same orientation and are parallel with respect to the coronal plane in the anterior-posterior direction, i.e., the rods/plates are coplanar from a lateral view, and the rods/plates are located at a fixed predetermined distance from one another.
Due to a wide variety of factors, the two rods or plates are rarely geometrically aligned in clinical situations. There are several ways to address variations from geometrical alignment. One way is to bend one or both of the rods or plates to accommodate its fixation by the transconnector. However, bending performed in either of the rods or plates is not always possible to achieve and can adversely affect the fixation thereof to the pedicle screws or hooks, etc. that are fixed to the spine, and can compromise the clinical outcome of the surgery. Furthermore, the bending can also adversely affect the mechanical properties or the rods/plates. Additionally or alternatively, the transconnector can be bent to address the geometrical misalignment of the rods/plates, so that the disturbance to the rod(s)/plate(s) positioning is minimized. However, bending of the transconnector can compromise the mechanical performance of the transconnector.
Adjustable transconnectors designed to adapt for variations from geometrical alignment have been provided. However, these transconnectors are multi-piece systems that can be difficult to assembly and use in the surgical environment. Further, there is no guarantee that this type of transconnector cannot become disassembled, losing one or more pieces, after implantation and closing of the patient. Still further, after such transconnectors are implanted (fixed to the rods/plates) there design does not take into account the spacing necessary to ensure that the implant does not engage the dura.
Adjustable connectors of one-piece design that are currently available do not allow for wide-range adjustments to compensate for all three modes in which there may be variation from geometric alignment: convergence or divergence, non-coplanar rods/plates, and variability on rod separation distances, while, at the same time, maintaining separation from the dura and the spinal cord.
There is a continuing need for transconnectors that are fully adjustable to compensate for all three modes of variation from geometrical alignment of the rods/plates being connected by the transconnector, which transconnectors do not pose a risk of disassembly of multiple parts or pose a challenge of assembling multiple parts, and which transconnectors maintain a safe distance, after implantation, from the dura and spinal cord, regardless of the position of the transconnector, the vertebral level where it is used or the span between the two rods/plates that the transconnector is joined to. The present invention meets at least all of the above needs.